Almost everyone will be familiar with the small built-in flashguns found on every type of compact camera. If you’re not, just turn the camera round and take a picture of your own face. Once your eyes have stopped watering, that bright green blob you’re now trying to blink out of your field of vision is the exact shape of your flashgun, so just look on the front of your camera for a clear window of the same shape. It may take several tries to get this right.